Add instructions on how to debug a crashed pod

When I was using `kubeadm init`, I ran into an issue where I had passed an
invalid flag through the kubeadm config file. The flag was being passed into
apiserver and preventing it from launching with a "unknown flag" error.

The flag in question is (other flags elided for clarity):

```
admission-control: ...,GenericAdmissionWebhook,...
```

Since this prevented the apiserver from coming up, the setup timed out
and gave me the error message I just modified.

It would be better if the config was vetted more thoroughly, but I think
documenting the backup strategy for viewing logs in case of failure is
also valuable.

cmd/kubeadm/app/cmd/init.go

@@ -103,6 +103,13 @@ var (
 		If you are on a systemd-powered system, you can try to troubleshoot the error with the following commands:
 			- 'systemctl status kubelet'
 			- 'journalctl -xeu kubelet'
+		
+		Additionally a service may not have come up in docker. If that's the case, you can enumerate all docker
+		containers that have been started (including ones that have crashed and exited) by running the following commands:
+			- 'docker ps -a'
+		
+		Once you have that list, you can inspect the logs for any job with:
+			- 'docker logs $INSTANCEID'
 		`)))
 )